The present invention relates to a magnetic recording medium, a method of producing the same, and a recording/reading-out method. The magnetic recording medium according to the present invention comprises at least a magnetic layer, optionally by means of an under layer, on a non-magnetic substrate, which has a satisfactory CSS (contact start and stop) characteristic and excellent sticking property of the magnetic head to the surface of the magnetic recording medium, and which can lower a flying height of the magnetic head.
Usually, information is written into and read out of a magnetic recording medium (disc) by means of a magnetic head, in which the disc is moved at a high speed to rise the magnetic head on the surface of the magnetic recording medium. In the disc, fabrication for applying mechanical polishing treatment has been applied to leave a fabrication traces (hereinafter referred to as `mechanical texture`) for improving a magnetic characteristic. Usually, the mechanical texture is applied on the surface of the non-magnetic substrate or on an under layer such as an NiP plated or sputtered layer disposed thereon.
Along with the recent demand for increasing the amount of information, and for miniaturizing and the lightweighting the device, the linear recording density and track density are increased, so that scratches caused by the existent mechanical texture result in an error at a high probability if the area per one bit is decreased.
Accordingly, it has been proposed a method of applying the mechanical texture only in a CSS region of the disc while leaving a data recording region as it is stand, but the surface of the data recording region is made higher than the height for the surface of the CSS region to bring about a problem that the magnetic head crushes upon seeking.
Further, a method of preparing a texture pattern by laser beam has also been proposed instead of the mechanical texture. For instance, U.S. Pat. Nos. 5,062,021 and 5,108,781 propose an attempt of locally melting or fusing an NiP layer by a Q switch laser beam of Nd-YAG, in which a pulse width is very narrow and an energy density is very high, and forming a center depression surrounded by a circular raised rim, thereby improving the CSS characteristic with respect to the magnetic head by the formed circular rim.
However, in the above-mentioned method, the contacting area with respect to a lower surface of the magnetic head is not decreased outstandingly, and it can not be said that the problem of sticking between the magnetic head and the disc is improved more as compared with the mechanical texture.
Further, a method of forming projections by using photolithography has also been proposed. For instance, a pretext for Tribology by published in The Japan Society of Tribologists (1991-5, A-11), (1992-10, B-6) shows the result of a CSS test for a disc having concentric projections formed by photolithography at 0.1 to 5% area ratio relative to the entire surface of the disc.
However, since the top of the projection is flat in the above-mentioned method, it involves a drawback that the frictional force is increased along with the sliding cycles of the magnetic head and that industrial application is not easy.
As a result of the present inventors' earnest studies, it has been found that by irradiating, to the surface of a non-magnetic substrate, a magnetic layer, an under layer or a magnetic medium, an energy beam that moves relatively to the said surface thereof and melting locally the said surface thereof, thereby forming projections on the surface, the thus obtained magnetic recording medium, wherein projections formed by irradiation of the energy beam and having a height of 1 to 60 nm are provided at the number of 10.sup.2 to 10.sup.8 per 1 mm.sup.2 on the surface of any one of the non-magnetic substrate, the under layer, the magnetic layer and the magnetic recording medium, is capable of preventing a magnetic head from sticking and reducing fluctuations for stable flying height of the magnetic head when the magnetic head seeks between the data recording region and the CSS region, and causing neither head crush nor instabilization of the magnetic head in a space. The present invention has been attained on the basis of the above-mentioned finding.